Ambulatory pumps or infusors are well known in the art. Such devices are used for delivering a predetermined quantity of a drug or other medicament to a patient in a preselected time period at a substantially constant fluid flow rate. One known pump includes a tubular, elastomeric, pressurized bladder that contains the liquid to be infused. The bladder is pressurized by the liquid stored therein. The pump includes a housing, a plug fixed in one end of the housing and an aperture that extends through the plug. One end of the bladder is sealingly attached to the plug, with the lumen of the bladder communicating with the aperture of the plug. The pump includes a conduit, such as a tube set connected to the plug aperture that defines a dispensing passageway for transporting the liquid from the bladder to the infusion site for the patient.
A flow regulator is disposed within the dispensing passage way for permitting the liquid to flow from the bladder through the dispensing passageway, to, for example, a patient, at a predetermined rate. The flow regulator or restrictor includes a capillary element.
The pump includes a "floating" or movable cap or indicator affixed to a free end of the bladder. The indicating member floats or moves longitudinally within the housing dependent upon the fill of the bladder. The indicating member includes a passageway, a one-way valve positioned at about the passageway and inlet or fill port through which the bladder is filled. The port and passage are in flow communication with the bladder.
In order to fill the bladder it is necessary to grasp the indicator by pinching or inwardly flexing the sides of the housing and inserting a fill device such as a syringe into the housing. The syringe is then connected to the fill port and the liquid is transferred from the syringe into the bladder. Typically, the syringe to fill port connection includes a threaded portion which forms a tight seal between the syringe and the fill port. As the bladder is filled, the indicating member is allowed to move to accommodate the expanding bladder.
While this known pump works well for its intended purpose, there are a number of drawbacks. First, the exterior of the bladder is essentially open to atmosphere by virtue of the floating characteristics of the indicator. Thus, in the event that the bladder ruptures, the liquid from the bladder will escape into the housing. An end cap positioned on the housing retains the liquid in the housing in the event of bladder rupture. However, the end cap is typically packaged separately from the housing, and, if improperly positioned on the housing, can result in leakage from the housing if the bladder ruptures.
In addition, the "floating" nature of the indicator can at times make it difficult to fill the infusion device because the indicator must be grasped through the housing wall. Because the indicator "floats" the bladder can be twisted as the syringe is threaded onto the inlet port. As will be apparent, twisting the elastomeric bladder can weaken the elastomeric material, thus increasing the opportunity for rupture. In addition, problems have been encountered that, it is believed, are a result of turbulence in the liquid during filling of the pump. Specifically, as the liquid "breaks" through the one-way valve, the flow resistance causes turbulence in the liquid, which, in turn, results in the entrainment of air in the liquid. The entrained air forms microbubbles in the liquid. It has been observed that these microbubbles can accumulate at the capillary in the flow restrictor. Those skilled in the art will recognize that the microbubble accumulation can result in blockage of fluid flow through the capillary.
Accordingly, there continues to be a need for an ambulatory pump that fully encloses the infusion bladder, which facilitates filling of the storage bladder and minimizes the opportunity to rupture the bladder. Such a device will be readily used with standard medical apparatus hardware, and will reduce the priming problems and flow restrictions encountered in known pump devices.